Apollo Lunar Module

• 1. Introduction

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  The Apollo Lunar Module is the only crewed vehicle in history to land somewhere beyond Earth. That fact alone is worth sitting with. Not a probe, not a robot, not a satellite. A vehicle carrying human beings. And it went somewhere no human vehicle has gone before or since.

  It was never meant to be beautiful. Structurally incapable of flying through Earth's atmosphere, it could not glide or soar. It was built for a single brutal task: dropping two people from lunar orbit to the Moon's surface, then firing them back up to rejoin their crewmate waiting above. It did that job six times, between 1969 and 1972.

  But the Lunar Module was more than a transport. On one mission, it kept three men alive when their main spacecraft was crippled. On others, it pushed the limits of how long humans could survive on another world. Its development was plagued with problems, its cost eventually reached $21.65 billion in 2016 dollars, and three of the training aircraft built to help astronauts practice landing it crashed. Every pilot who flew those trainers survived, though barely. One of them was the man who would become the first human to walk on the Moon.

• 2. A Decision That Demanded a New Vehicle

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  NASA did not always plan to build a separate lunar lander. The original approaches to reaching the Moon involved either flying a complete spacecraft directly to the surface, or assembling the mission vehicle in Earth orbit first. Either way, a single, heavier craft would have handled the entire journey, including landing.

  The choice of Lunar Orbit Rendezvous changed everything. Once NASA committed to that method, it became necessary to produce a small dedicated craft that could detach from the main spacecraft in lunar orbit, descend to the surface, and ascend back to rejoin the command module waiting above. A separate lander was not a preference; it was a logical requirement of that decision.

  In July 1962, eleven firms were invited to submit proposals for what was then called the Lunar Excursion Module, or LEM. Nine companies responded in September, each answering twenty questions posed by NASA in a sixty-page technical proposal. Grumman won the contract officially on the 7th of November 1962. The expected cost at that point was around $350 million. What followed was far more expensive and far harder than anyone anticipated.

  Four major subcontractors came aboard early on: Bell Aerosystems handled the ascent engine, Hamilton Standard the environmental control systems, Marquardt the reaction control system, and Rocketdyne the descent engine. The guidance computer was manufactured by Raytheon, working from designs developed at the MIT Instrumentation Laboratory. A backup navigation tool called the Abort Guidance System was developed by TRW. The landing gear itself was manufactured by Heroux. All of this assembly took place at a Grumman factory in Bethpage, New York.

• 3. Designing Something Entirely New

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  Thomas J. Kelly, a Grumman aerospace engineer, was the chief designer of the Apollo Lunar Module. He did not have much precedent to draw from. Nothing quite like this had ever been built.

  The earliest design looked like a shrunken version of the command and service module: a cone-shaped cabin sitting atop a cylindrical propulsion section, with folding legs. The second attempt borrowed from helicopter design, with large curved windows and seats to help the crew see the surface while hovering and landing. That version also included a forward docking port so the lander crew could take an active role in connecting with the command module.

  Neither design survived long. Weight was the enemy of everything. The curved windows and seats went first; the astronauts would stand while flying, held by a cable and pulley system, with smaller triangular windows providing just enough view of the landing site. The forward docking port was eventually removed too, which meant the commander lost active control of docking and had to rely on a small overhead window to watch the command module approach.

  Landing gear went through its own evolution. Three legs were the lightest option, but also the most dangerous: if one leg hit at a bad angle, the whole vehicle could tip. Five legs were the most stable, but too heavy. Four was the compromise. The configuration was frozen in April 1963.

  Power sources were reconsidered as well. Fuel cells were the original plan, similar to those used in the command module. In March 1965, they were abandoned entirely in favor of batteries. And the name changed too. In June 1966, NASA dropped the word "excursion," officially renaming the vehicle the Lunar Module. According to George Low, who managed the Apollo Spacecraft Program Office, NASA worried that "excursion" made the whole enterprise sound frivolous. The astronauts and engineers kept calling it the LEM anyway.

• 4. Learning to Land

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  Gus Grissom said in 1963 that landing on the Moon was essentially a hovering operation, and he wondered aloud whether the first person to do it should be a highly experienced helicopter pilot rather than a fighter pilot. Most early astronauts came from fighter aviation. Landing a lunar module on the Moon would require something closer to the feel of a helicopter, though no helicopter had ever operated in one-sixth gravity with no atmosphere.

  NASA contracted Bell Aerosystems in 1964 to build a training vehicle called the Lunar Landing Research Vehicle, known as the LLRV. It worked by using a gimbal-mounted vertical jet engine to cancel out five-sixths of its own weight, simulating the Moon's weaker gravity, while hydrogen peroxide thrusters mimicked the LM's descent engine and attitude control. Testing two LLRV prototypes at the Dryden Flight Research Center went well enough that three production Lunar Landing Training Vehicles, or LLTVs, were ordered in 1966 and added to the training program at the Houston Manned Spacecraft Center.

  Three of the five total aircraft were destroyed in crashes. In each case, the rocket-powered ejection seat saved the pilot. One of the pilots who ejected from a crashing LLTV was Neil Armstrong, who would become the first person to walk on the Moon.

  The design of the lunar lander itself had been adjusted to account for the realities of landing. The original plan called for contact sensor probes on all four landing legs. Beginning with LM-5 on Apollo 11, the probe on the leg nearest the ladder was removed. The concern was that a probe bent by touchdown might protrude upward and puncture an astronaut's suit as he climbed down to the surface.

• 5. From Testing to the Moon

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  LM-1 was built specifically for an uncrewed test flight to check its propulsion systems, launched into low Earth orbit on a Saturn IB. That flight had been planned for April 1967. Development problems pushed it to the 22nd of January 1968, as Apollo 5. LM-2 had been held in reserve in case LM-1 failed; it was not needed.

  LM-3 became the first crewed lunar module, flown in low Earth orbit as Apollo 9 on the 3rd of March 1969, to test all systems and practice the separation, rendezvous, and docking maneuvers. A second crewed practice flight in higher Earth orbit had been planned but was cancelled to protect the program's schedule. Apollo 10 launched on the 18th of May 1969 using LM-4, nicknamed Snoopy, as a full dress rehearsal in lunar orbit, descending to within 47,400 feet of the lunar surface before returning to the command module.

  The first crewed lunar landing came on the 20th of July 1969, when LM-5 Eagle set down in the Sea of Tranquility. Four days later, the crew splashed down in the Pacific Ocean in the command module Columbia, completing what President John F. Kennedy had called the national goal of landing a man on the Moon and returning him safely to Earth before the decade was out.

  Apollo 12 followed with LM-6 Intrepid at the Ocean of Storms. Then came one of the most dramatic moments in spaceflight history. In April 1970, an oxygen tank in the Apollo 13 service module ruptured, disabling the main spacecraft. LM-7 Aquarius, designed to support two astronauts for 45 hours, was pressed into service as a lifeboat for three astronauts for 90 hours. Its descent engine substituted for the crippled main propulsion system. Its batteries powered the spacecraft home and recharged the command module's own batteries for reentry. The crew splashed down safely in the South Pacific Ocean on the 17th of April 1970.

• 6. Extended Missions and Final Flights

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  Apollo 15, 16, and 17 flew with an upgraded version called the Extended Lunar Module. The descent engine received a 10-inch extension added to the engine bell, and the descent propellant tanks were enlarged. A waste storage tank was added to the descent stage. These changes allowed crews to stay on the Moon for up to 75 hours, compared with 48 hours for the earlier missions.

  The Lunar Roving Vehicle traveled to the Moon folded up and stored in Quadrant 1 of the descent stage, deployed by the astronauts after landing. On these extended missions, the communications antenna and television camera were mounted on the rover rather than set up separately. The return payload from Apollo 17 included as much as 238 pounds of lunar rock and soil samples.

  Hover times on the final four landing missions were extended by a technique begun on Apollo 14: using the service module engine to perform the initial descent orbit insertion burn 22 hours before the lunar module separated from the command module. This left the lander with a full load of descent propellant for the powered approach, and additional reserve fuel for the final phase of landing.

  The last lunar module to fly was LM-12 Challenger, part of Apollo 17, which launched on the 7th of December 1972. Its descent stage remains at the Taurus-Littrow landing site on the Moon. Its ascent stage was deliberately crashed into the lunar surface to generate readings from seismometers already placed there by earlier crews. LM-13, which had been intended for Apollo 19 and was partially completed by Grumman, later appeared in the 1998 miniseries From the Earth to the Moon, standing in to depict earlier vehicles including Eagle.

• 7. What Survived

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  Six descent stages are still sitting on the Moon, exactly where they landed. Their ascent stages were either crashed into the lunar surface or, in the case of Apollo 11's Eagle, left in lunar orbit where it may still be circling today.

  Apollo 10's ascent stage, nicknamed Snoopy, followed a different path. After its descent stage was jettisoned in lunar orbit, Snoopy's ascent engine was fired until its fuel ran out, sending it past the Moon into a heliocentric orbit around the Sun. It is the only flown lunar module ascent stage known to have survived intact. Astronomers have since identified asteroid 2018 AV2 as a possible candidate for Snoopy's current location.

  Of the lunar modules that never flew, several are on public display. LM-2, intended as a backup for the first uncrewed test, ended up at the National Air and Space Museum in Washington, D.C. LM-9, which was slated for Apollo 15 before being replaced by the Extended Lunar Module, is at the Kennedy Space Center. LM-13 is on display at the Cradle of Aviation Museum on Long Island, New York, not far from the Grumman factory in Bethpage where all the lunar modules were assembled.

  The total development and production cost of the Lunar Module program reached $2.29 billion in nominal dollars, equivalent to $21.65 billion adjusted to 2016 values using the NASA New Start Inflation Indices. What that money produced was a spacecraft with no wings, no aerodynamic surfaces, and no ability to fly in any atmosphere. It could only exist in space. And in the vacuum between the Moon's orbit and its surface, it became, as the source notes, the most reliable component of the entire Apollo-Saturn space vehicle.